Through Casing Coring

ABSTRACT

Devices and methods for obtaining core samples from a formation that surrounds a cased wellbore. A coring tool includes a casing cutter for cutting an opening in the casing and a coring device for obtaining a core sample from the formation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to devices and methods for obtainingcore samples from the sidewall of a cased wellbore. The device is alsouseful for obtaining cores from the sidewall of an openhole wellbore.

2. Description of the Related Art

Coring devices are more typically known for obtaining core samples fromthe uncased sidewall of a wellbore. The inventors have recognized thatthere might be an to advantage to evaluating certain formation zonesafter a well has been cased.

SUMMARY OF THE INVENTION

The invention provides devices and methods for obtaining core samplesfrom the sidewall of a cased wellbore. In a described embodiment, acoring tool is provided includes an outer housing that encloses aplurality of bit boxes. The bit boxes are moveable within the housing sothat they may be selectively aligned with an opening in the outerhousing. In a particular embodiment, the bit boxes are contained withina carriage that is axially moveable within the outer housing betweenseparate operational positions wherein the tools within the bit boxesare selectively aligned with a portion of the wellbore from which it isdesired to obtain a core sample.

In certain embodiments, the housing contains a first bit box with acasing cutter having a casing cutting bit that is suitable for cuttingthrough the surrounding casing and cement. The housing preferably alsocontains a second bit box with a coring device having a coring bit thatis suitable for cutting and obtaining a core sample from the surroundingformation. Preferably also, the coring device can articulate or moveangularly to separate the core sample from the formation. The separatedcore sample is preferably deposited into a coring tube or receptaclewithin the coring tool housing.

In particular embodiments, the coring tool contains a third bit box thatincludes a device for placement of a casing plug into the opening thatwas previously cut into the casing.

According to a further preferred feature of the invention, the carrieris rotatable to within the outer casing of the coring tool. An operatorcan rotate the carrier within the coring tool housing in order to obtaincore samples from other angular locations within the wellbore. A coringtool in accordance with the present invention can preferably be disposedwithin a wellbore on wireline conveyance. Power and data communicationwith the coring tool can then be conducted via the wireline. Inparticular embodiments, the coring tool includes an electronic and powersection that controls and provides power to the casing cutter device,the coring device and the hole plugging subassembly. In addition, thecoring tool preferably includes a power transfer medium for movement ofthe carriage within the coring tool outer housing.

The invention provides methods for obtaining coring samples from casedwellbores. In exemplary operation, a coring tool is disposed into acased wellbore to a depth or location at which it is desired to obtainone or more core samples. Stabilizers may be set within the wellbore tosecure the coring tool in place within the wellbore. Thereafter, thecarrier is axially moved within the outer housing of the coring tool soas to selectively align first the casing cutter device and then thecoring device so that each of these tools can operate at a preselectedlocation and a core sample is obtained. If desired, the carrier is thenmoved axially within the outer housing to align the hole pluggingsubassembly with the opening that was previously formed in the casing.The hole plugging subassembly is then operated to secure a plug withinthe opening in the casing. The devices and methods of the presentinvention allow for multiple cores to be obtained from multiplelocations.

BRIEF DESCRIPTION OF THE DRAWINGS

For a thorough understanding of the present invention, reference is madeto the following detailed description of the preferred embodiments,taken in conjunction with the accompanying drawings, wherein likereference numerals designate like or similar elements throughout theseveral figures of the drawings and wherein:

FIG. 1 is a side, cross-sectional view of an exemplary cased wellborewith an exemplary coring tool disposed therein which is constructed inaccordance with the present invention.

FIG. 2 is an enlarged side, cross-sectional view of portions of thecoring tool shown in greater detail and being used to form an opening inthe wellbore casing.

FIG. 3 is a side, cross-sectional view of the portions of the coringtool of FIG. 2, now in an operational configuration to obtain a coresample from surrounding formation.

FIG. 4 is a side, cross-sectional view of the portions of the coringtool shown in FIGS. 2 and 3, now in a configuration for plugging anopening previously created in the surrounding casing.

FIG. 5 is a detail view depicting a core sample being obtained by acoring bit.

FIG. 6 is a schematic axial cross-sectional view illustrating exemplaryrotation of a bit box carrier within the coring tool outer housing.

FIG. 7 depicts an alternative embodiment for an exemplary coringarrangement wherein the coring tool is moved within the wellbore toreposition cutting, coring and plugging components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts an exemplary wellbore 10 that has been drilled throughthe earth 12 from the surface (not shown). The wellbore 10 is surroundedby a formation 14 at a lo depth from which it is desired to obtain oneor more sidewall core samples. The wellbore 10 is lined with a metalliccasing 16 which has been secured in place with cement 18.

A coring tool 20 has been disposed within the wellbore 10 by wireline22, in a manner known in the art. The coring tool 20 includes agenerally cylindrical outer housing 24 that encloses the variouscomponents used to accomplish coring, as will be described. An opening26 is formed in the outer housing 24. Stabilizers 28, of a type known inthe art, have been extended radially outwardly from the coring tool 20to secure it within the wellbore 10. Preferably, the stabilizers 28maintain the coring tool 20 in proximity to one side of the wellbore 10.

FIG. 2 depicts interior components of an exemplary coring tool 20 as thecoring tool 20 is being used to cut an opening in the casing 16 andcement 18 lining the wellbore 10. The coring tool 20 includes anelectronics and power section, indicated schematically at 30. Theelectronics and power section 30 receives electrical power for thecoring tool 20 via the wireline 22. The electronics and power section 30may be electrically coupled to any of the components in the coring tool20 requiring electrical power to operate. Also, the electronics andpower section 30 may include any number of electrical components tofacilitate operation of coring tool components. As depicted in FIG. 2,the electronics and power section 30 includes a processing system 32having at least one information processor 34 of a type known in the artfor actuation and control of the various components of the coring tool20. The electronics and power section 30 also includes transmitter andreceiver circuits 36 to convey information to surface and to receiveinformation and commands from the surface via a wireline communicationcable. Additionally, the electronics and power section 30 includes amemory unit 38 for storing programs and information processed by theprocessor 34 in order to operate the various components of the coringtool 20. The electronics and power section 30 may also includeelectronic components used for cooling, radiation hardening, vibrationand impact protection, potting and other packaging details that do notrequire in-depth discussion as they are known in the art. A data bus 40is used to communicate information between the various components of theelectronics and power section 30 as well as externally to a powertransfer medium 42.

The electronics and power section 30 is operably associated with a powertransfer medium, schematically shown at 42. The power transfer medium 42may be selected according to the particular power generating devicesused to actuate and position bit boxes within the coring tool housing24. The power transfer medium 42 may be a hydraulic fluid conduit wherethe power transfer device includes a hydraulic pump. The power transfermedium 42 may be an electrical conductor where the power generatingdevice includes an electrical power generator. Alternatively, the powertransfer medium 42 may be a drive shaft or gearbox where the powergenerating device includes a mechanical power output for extending atool radially outwardly from the coring tool 20.

A bit box carriage 44 is retained within the coring tool 20 and isaxially moveable and repositionable within the coring tool housing 24between multiple operational positions. In order to ensure properalignment and prevent undesirable radial movement of the bit boxcarriage 44, a guide rail or track (not shown), of a type known in theart, may be incorporated into the coring tool housing 24 along which thebit box carriage 44 can slidably move. One example of a suitable guiderail arrangement would be an opposing pair of rigid plates. Each of theplates would have an elongated slot formed therein, while the bit boxcarriage 44 would have complimentary lugs that would ride within theseslots. However, other suitable guide rail or track arrangements couldalso be used to help ensure precision alignment and movement of the bitbox carriage 44 within the housing 24. The bit box carriage 44 depictedin FIG. 2 contains two individual bit boxes: a casing cutter bit box 46and a coring bit box 48. The bit boxes 46 and 48 are each adapted toorient and extend a cutting tool radially outwardly from the coring tool20 through opening 26. In certain embodiments, the bit box carriage 44also includes a hole plugging subassembly 50 that is located in aseparate box 52 within the carriage 44. The bit box carriage 44 can bemoved axially within the coring tool housing 24 by the power transfermedium 42, which in turn may be actuated and controlled by theprocessing system 32 in accordance with a preprogrammed scheme. In FIG.2, the bit box carriage is oriented within the coring tool housing 24such that the casing cutter bit box 46 is aligned with the opening 26 ofthe coring tool housing 24.

The casing cutter bit box 46 includes a casing cutter in the form of acasing cutting mill bit 54 that is mounted upon a rotary cutting device56. The rotary cutting device 56 is capable of rotating the cutting millbit 54 and extending it radially outwardly through the opening 26 andinto cutting engagement with the casing 16 lining the wellbore 10. Thecasing cutting mill bit 54 is preferably a generally cylindrical cutterwith an open center portion that is capable of forming a circular cutwithin the casing 16 and the cement 18. When the casing cutting mill bit54 cuts through the casing 16 and cement 18, the cutaway portions willtypically be retained within the open center portion of the bit 54 inthis instance. Alternatively, the cutting mill bit 54 might be a drilltip type cutter which forms an opening in to the casing 16 and cement 18in the manner of a rotary drill. In certain embodiments, the rotarycutting device 56 may also swivel to allow the cutting mill bit 54 to berotated between a position wherein the bit 54 is facing away from theopening 26 (see phantom position 54 a) and a position wherein the bit 54is facing toward the opening 26 and can be extended toward the casing16.

The coring bit box 48 is preferably located axially below the casingcutter box 46 within the chassis 44. Also, the coring bit box 48preferably includes an opening 58 along its lower side so that capturedcores can be released into a core tube 60 within the coring tool housing24. The coring tool bit box 48 retains a coring device in the form of acoring bit 62 which is capable of cutting and capturing a core samplefrom the formation 14. Suitable coring bits for this purpose aredescribed in U.S. Pat. No. 7,373,994 entitled “Self Cleaning Coring Bit”and issued to Tchakarov et al. This patent is owned by the assignee ofthe present application and is hereby incorporated by reference in itsentirety. The coring bit 62 is mounted upon a rotary cutting device 64.The rotary cutting device 64 is capable of rotating the coring bit 62and extending it radially outwardly through the opening 26 and intocutting engagement with the formation 14 to obtain a core sample.Additional details relating to the operation of rotary coring tools toobtain a core sample from a wellbore sidewall are described in U.S. Pat.No. 7,530,407 issued to Tchakarov et al. This patent is owned by theassignee of the present application and is hereby incorporated byreference in its entirety. Suitable rotary cutting devices for thispurpose include the MaxCOR™ rotary sidewall coring system that isavailable commercially from Baker Hughes Incorporated of Houston, Tex.

The hole plugging subassembly 50 includes a magazine 66 which containsone or more circular plugs 68. Each of the plugs 68 is shaped and sizedto close of an opening in the casing 16 that has been cut by the casingcutting mill bit 54. In addition, the hole plugging subassembly 50includes an extendable piston assembly 70 that can urge the plugs 68within the magazine 66 outwardly so that the outermost plug 68 is seatedwithin such a milled opening.

The bit box carriage 44 is selectively moveable between axialoperational positions within the housing 24 in order to position thecarriage 44 to enable it to perform operations that will permit a coresample to be obtained from a cased wellbore 10 These positions areillustrated by FIGS. 2, 3 and 4. In FIG. 2, the carriage 44 ispositioned in a first operational position so that the casing cutter bitbox 46 is located proximate the opening 26 in the housing 24 to allowthe casing cutting mill bit 54 to cut an opening in the casing 16 andcement 18 at a desired target position Once an opening is formed in thecasing 16 and cement 18, the casing cutting mill bit 54 is withdrawnback into the coring tool outer housing 24. The bit box carriage 44 isthen axially shifted by the power transfer medium 42 from the firstoperational position shown in FIG. 2 to a second operational position,as illustrated in FIG. 3.

When the coring tool 20 is in the second operational position shown inFIG. 4, the coring bit box 48 is generally aligned with the opening 26in the coring tool housing 24. As depicted in FIG. 3, the rotary cuttingdevice 64 rotates the coring bit 62 and extends the coring bit 62outwardly through the opening 26 and into cutting engagement with theformation 14. As FIG. 5 depicts, a core sample 72 is formed as thecoring bit 62 creates a circular cut 74 in the formation 14.Articulation or angular movement of the shaft 76 that retains the coringbit 62 (as illustrated at 78) will break off the core sample 72 from thelo formation 14. The core sample 72 can then be ejected into the coretube 60 The core sample 72 will be brought to the surface when thecoring tool 10 is withdrawn from the wellbore 10.

FIG. 4 illustrates the coring tool 20 in a third operationalconfiguration wherein the carriage 44 has been aligned by the powertransfer medium 42 so that the box 52 is aligned with the opening 26 inthe coring tool housing 24. The piston assembly 70 urges the stack ofplugs 68 radially outwardly until the outermost plug 68 is seated intothe opening 80 that was formed in the casing 18. The plug 68 ispreferably secured within the opening 80 by an interference fit. It isnoted that this step of plugging the opening 80 in the casing 18 is notalways required. If the coring operation is being performed, forexample, in a formation zone wherein production is already occurringthrough perforated casing 16, then it is unnecessary to plug the opening80.

In particular embodiments of the present invention, the coring tool 20is capable of obtaining multiple core samples from the wellbore 10. Inaddition, the coring tool 20 is preferably capable of plugging multipleopenings 80 formed within the casing 16 of the wellbore 10. According toan exemplary embodiment, the carriage 44 is capable of axial rotationwith respect to the outer housing 24 of the coring tool. A torsionalmotor 82 applies rotational force to the carriage 44 to rotate itangularly within the housing 24. FIG. 6 illustrates an embodiment forthe coring tool 10 wherein there are multiple openings 26 in the outerhousing 24. Rotation of the carriage 44 thereby allows the cutting tools54, 62 to be angularly aligned with each of the openings 26 a, 26 b, 26c, or 26 d. Although there are four openings 26 a, 26 b, 26 c, 26 dshown in FIG. 6, it should be understood that there may be more or fewerthan four such openings. The carriage 44 may be rotated in the angulardirections indicated by arrows 84 in FIG. 6. This feature permits thecarriage 44 to be repositioned so that it can obtain further coresamples.

If it is desired to obtain core samples from other depths or locationswithin the wellbore 10, the stabilizers 28 can be unset and the coringtool 20 then raised or lowered to another depth or location within thewellbore 10 from which it is desired to obtain further core samples.Thereafter, additional core samples can be obtained in the mannerpreviously described.

According to an exemplary method of operation, the coring tool 20 isdisposed into the wellbore 10 to a depth or location within the casedwellbore 10 from which it is desired to obtain one or more core samples72. The stabilizers 28 are then set to secure the coring tool 20 inplace within the wellbore 10. The carriage 44 is positioned in the firstoperational position depicted in FIG. 2. This may occur prior to runningthe coring tool 20 to its desired depth or afterward. The rotary cuttingdevice 56 is actuated so that the casing cutting bit 54 cuts an opening80 in the casing 16 of the wellbore 10. The carriage 44 is moved to thesecond operational position depicted in FIG. 3. The rotary cuttingdevice 64 then operates the coring bit 62 to obtain a core sample 72from the formation 14 that lies radially outside of the casing 16 andcement 18. The core sample 72 is then disposed into a core tube 60 orother core sample receptacle. The carriage 44 may then be moved to thethird operational position depicted in FIG. 4. The hole pluggingsubassembly 50 is then actuated to close off the opening 80 in thecasing 16. If desired, an operator can then rotate the carriage 44within the outer housing 24 to align with other openings, such as 26 b,26 c or 26 d and obtain additional coring samples.

FIG. 7 illustrates an alternative arrangement for obtaining a core froma cased wellbore 10. An exemplary coring tool 90 is disposed within thewellbore 10 by wireline 22 suspension. The coring tool 90 includes anouter housing 92 which contains bit boxes 46, 48 which are preferablyfixed against axial movement with respect to the outer housing 92. Inaddition, the coring tool 90 preferably contains a hole pluggingsubassembly 50. The outer housing 92 is provided with three lateralopenings 94, 96, 98. Opening 94 is aligned with the casing cutter rotarycutting device 56 so that the casing cutting mill bit 54 may be extendedradially outwardly through the opening 94. The mill bit 54 can cut anopening in the casing 16 when aligned with a target point 100 (shown inphantom in FIG. 7) within the wellbore 10. Opening 96 is aligned withthe rotary cutting device 64 so that the coring bit 62 can be extendedradially outwardly through the opening 96. The coring bit 62 can obtaina core sample, as described above, when the opening 96 is aligned withthe target point 100. Opening 98 is aligned with the hole pluggingsubassembly 50. The hole plugging subassembly 50 can emplace a plug 68within a previously-milled opening within the casing 16 when the opening98 is aligned with the target point 100.

In operation, the coring tool 90 is moved axially upwardly anddownwardly within the wellbore 10 via wireline manipulation, asillustrated by arrows 102 in order to align the appropriate lateralopenings 94, 96 or 98 with the target position 100 in order toaccomplish the tasks to obtain a core sample from the target position100 of the wellbore 10. First, the coring tool 90 is positioned withinthe wellbore 10 so that the opening 94 is aligned with the targetposition 100. Reversible slips or anchors (not shown) of a type known inthe art may be used to secure the coring tool 90 in this position.Thereafter, the rotary cutting device 56 is actuated to cut an openingin the casing 16. The coring tool 90 is then repositioned in thewellbore 10, moving the coring tool 90 with the wireline 22 until theopening 96 is aligned with the target position 100. Again, reversibleslips or anchors may be used to secure the coring tool 90 in thisposition. The cutting device 64 is actuated so that the coring bit 62extends through the opening in the casing 16 to obtain a core samplefrom the surrounding formation. Next, the coring tool 90 is moved bywireline 22 until the opening 98 is aligned with the target position100. Next, the hole plugging subassembly 50 is actuated to emplace aplug 68 within the previously-formed opening in the casing 16.Thereafter, one can remove the coring tool 90 from the wellbore 10 viawireline retrieval.

Those of skill in the art will recognize that numerous modifications andchanges may be made to the exemplary designs and embodiments describedherein and that the invention is limited only by the claims that followand any equivalents thereof.

What is claimed is:
 1. A coring tool for obtaining a core sample from aformation surrounding a cased wellbore, the coring tool comprising: acasing cutter for cutting an opening in casing lining the wellbore; anda coring device for obtaining a core sample from the formation.
 2. Thecoring tool of claim 1 further comprising a hole plugging subassembly toclose off said opening in the casing lining the wellbore.
 3. The coringtool of claim 1 wherein: the coring tool has an outer housing having anopening therein; and the casing cutter and the coring device areretained within a carrier that is moveable within the outer housingbetween a first operational position wherein the casing cutter isaligned with the opening in the coring tool housing and a secondoperational position wherein the coring device is aligned with theopening in the coring tool housing.
 4. The coring tool of claim 3wherein the carrier is rotatable within the casing tool housing.
 5. Thecoring tool of claim 1 wherein the casing cutter comprises a casingcutting mill bit that is mounted upon a rotary cutting device.
 6. Thecoring tool of claim 1 wherein the coring device comprises a coring bitthat is mounted upon a rotary cutting device.
 7. The coring tool ofclaim 1 wherein: the coring tool is positioned by wireline manipulationto align the casing cutter with a target position within the wellborefrom which it is desired to obtain a core sample; and the coring tool isthen repositioned by wireline manipulation to align the coring devicewith the target position to obtain a coring sample from the targetposition.
 8. A coring tool for obtaining a core sample from a formationsurrounding a cased wellbore, the coring tool comprising: a casingcutter for cutting an opening in casing lining the wellbore; a coringdevice for obtaining a core sample from the formation; and a holeplugging subassembly to close off said opening in the casing lining thewellbore.
 9. The coring tool of claim 8 wherein: the coring tool has anouter housing having an opening therein; and the casing cutter and thecoring device are retained within a carrier that is moveable within theouter housing between a first operational position wherein the casingcutter is aligned with the opening in the coring tool housing and asecond operational position wherein the coring device is aligned withthe opening in the coring tool housing.
 10. The coring tool of claim 9wherein the carrier is rotatable within the casing tool housing.
 11. Thecoring tool of claim 8 wherein the casing cutter comprises a casingcutting mill bit that is mounted upon a rotary cutting device.
 12. Thecoring tool of claim 8 wherein the coring device comprises a coring bitthat is mounted upon a rotary cutting device.
 13. A method of obtaininga core sample from a formation surrounding a cased wellbore, the methodcomprising the steps of: forming an opening in casing lining thewellbore; and obtaining a core sample from the formation.
 14. The methodof claim 13 further comprising the step of closing o the opening in thecasing.
 15. The method of claim 14 wherein the step of closing off theopening in the casing further comprises actuating a hole pluggingsubassembly to emplace a plug in the opening.
 16. The method of claim 13further comprising disposing the core sample in a core sample receptaclewithin the coring tool.
 17. The method of claim 13 wherein the step offorming an opening in the casing comprises rotating a casing cutting bitto form a circular cut within the casing.
 18. The method of claim 13wherein the step of obtaining a core sample comprises rotating a coringbit to form a cylindrical core sample and separating the core samplefrom the formation.
 19. The method of claim 13 wherein: the step offorming an opening in casing lining the wellbore further compriseslocating the casing cutter to be aligned with a target position fromwhich it is desired to obtain a core sample and actuating the casingcutter to cut an opening in the casing; and the step of obtaining a coresample from the formation further comprises locating the coring deviceto be aligned with the target position and actuating the coring deviceto obtain a core sample from the target position.
 20. The method ofclaim 19 wherein the coring device is located to be aligned with thetarget position by moving a bit box carriage within an outer housing ofthe coring tool.
 21. The method of claim 19 wherein the coring device islocated to be aligned with the target position by moving an outerhousing containing the coring device within the wellbore.